The present invention relates to a method and system for controlling the cooling of small milk quantities (milk spots) entering, with time intervals, a cooling tank having a first end wall, a second end wall and at least a bottom wall portion with a milk contacting cooling surface within the tank being part of a cooling circuit of a cooling equipment.
Milk extracted by means of a milking machine is conventionally pumped to a refrigerated cooling tank, e.g. a bulk tank for cooling and storing of the milk. During the storing in the cooling tank a cream separation occurs, which will render the milk inhomogeneous and aggravate sampling of the stored milk when fetched for transportation to e.g. the dairy. The milk samples are being used to establish the quality of the milk and are fundamental for the dairy""s payment to the milk producer.
The bulk tank is usually provided with agitator means for agitation of the milk in the tank. On one hand to improve the heat transfer from the milk to a milk contacting cooling surface within the tank, which cooling surface is a part of the cooling circuit of a cooling equipment, and on the other to prevent the formation of a cream-layer in the tank. The cooling tanks on the market are usually designed to be discharged every second day and should therefore be capable to store and cool one quarter (xc2xc) of the total volume within the relatively short period of time when the milking takes place. Principally, since milking conventionally occurs twice a day, said cooling equipment is not to be activated until said agitator means is immersed to a great deal in milk, after a sufficient milk quantity has been assembled in the tank.
A bulk tank of the above kind, being associated with a milking machine used in an automatic milking system (AMS), is therefore subject to an alteration of its fundamental design conditions. E.g. the milk flow will be relatively small and occurs intermittently twenty-four hours a day. Hence, during a period of several hours in connection with the emptying and cleaning of said tank, the milk will be introduced into said tank in milk spots, which form a thin layer only on the bottom of the tank. This will complicate the cooling management and further, when the milk level eventually has reached the agitator means, a cream layer will occur on top, which is highly sensitive to mechanical treatment (shearing). The fat content of the cream consists of emulsified fat particles or fat globes, which are surrounded by a protecting protein coating. If this coating is damaged (by means of mechanical treatment) in such an extent that the fat is freely exposed, an enzymatic breakdown takes place, which in turn generates the formation of free fatty acids, which will have a detrimental effect on the milk quality (bad taste). Further, if freezing occurs it will cause damage to both the casein micelles and fat content as well.
If the cooling equipment is allowed to run at full power and the agitator means is not capable of generating a flow, which is sufficient to ensure a good transmission of heat, there is an impending risk that said thin milk layer would freeze to ice. Then the fat emulsion would also be destroyed and the milk quality deteriorated.
To reduce said risk the power of the cooling equipment could be controlled e.g. as is described in our patent application SE 0000362-4, filed on Feb. 4, 2000. However, the refrigerating capacity would be further increased if the milk spots or thin milk layer were put in motion across the cooling surface in the tank.
It is therefore desirable to create an agitation of the incoming milk in the tank even at a low or non-existent milk level. A suitable equipment would be complementary to the regular agitator means in a present cooling tank associated with an AMS. One of the ideas (the main idea) is that conventional tanks easily can be adapted for AMS so that the farmer need not by a new tank. Thus would the agitators be the same. However, in the time interval immediately after emptying the volume is small and less agitating power and cooling power would be needed.
The cooling tank in question is in the shape of a lying cylinder and the cooling surface is part of its cylindrical envelope surface. Therefore, the milk layer is particularly thin at the outer regions of the cooling surface, which means an increased freezing risk. On the other hand, the refrigerant is introduced into the vaporiser, usually below the lowest part of the envelope surface of the tank at one of its end walls, where the milk layer can be expected to be thicker. However, as a rule the tank is arranged to incline towards its opposite end wall, where the outlet usually is arranged, in order to achieve discharging in an efficient way. Due to this fact, occasionally the milk layer will be particularly thin even over that part of the envelope surface of the tank below which the refrigerant is introduced, also with an increasing freezing risk as a result.
Consequently, for a considerable period of hours in connection with the emptying and cleaning of the tank, there will occur only a thin milk layer on the cooling surface within the tank. Said milk layer will be particularly thin at the outer regions of the cooling surface, which means an increasing freezing risk.
Therefore, it is desirable to achieve relatively long cooling sequences with a minimum of freezing risk even for small milk quantities. This might be achieved by decreasing the magnitude of cooling power and providing to a present magnitude of cooling power correspondingly controlled pumping sequences for the emptying of an end unit of a milking system into the tank.
An object of the invention is to solve the described problems with regard to previously known cooling tanks, by providing an improved method and system for cooling of small milk quantities.
One important factor of the invention is the period of time, during which the milk pump must be running, in order to transfer the milk extracted from one animal to the milk tank. Another important factor is the position in which the input tube is situated in the tank and its direction and thereby the direction of the input flows.
This has been solved by a method of the initially defined kind, which is characterised by the following steps:
a) providing an input means which is arranged for, after said cooling tank has been emptied and cleaned, inducing an intermittent milk flow of said small milk quantities across said milk contacting surface,
b) reactivating the cooling equipment upon occurrence of a milk flow, which by its own motion has a sufficient flow rate to prevent freezing of said small milk quantities for a corresponding magnitude of cooling power, and
c) using said input means for, after a sufficient amount of small milk quantities have been introduced to form a pool of milk on the bottom of the tank, agitation of said pool of milk by means of the hydraulic input of the incoming milk.
A corresponding system of the initially defined kind, is characterised in that an input means is provided, which is arranged with an agitation pipe having a nozzle end for introducing the incoming milk onto the milk contacting surface at a position, which is situated between said first end wall and a central part of the tank, said position being laterally displaced relative to the perpendicular central axis of the tank, and that said nozzle end of said input means is directed towards said second end wall of the tank.
Preferably, this is performed by arranging to the present magnitude of cooling power correspondingly controlled pumping sequences for the emptying of an end unit of a milking system into the cooling tank, after milking of each animal, and transporting milk from the under-pressure part or re-circulating milk from the cooling tank.
Suitably, said incoming milk is drawn from said pool of milk by pumping means.
Advantageously, this can be achieved by arranging said input means for inducing a rotatory movement of said pool of milk.
Suitably, this is possible by arranging said input means with at least one agitation pipe for introducing said hydraulic input of the incoming milk laterally displaced in the tank.
Preferably, this can be achieved by inserting an agitation pipe to be extended through a regular milk outlet of the tank.
Advantageously, this is performed by directing a nozzle end of said agitation pipe towards said second end wall of the tank, for introducing the incoming milk in said direction and essentially parallel to the bottom wall portion of the tank.
Suitably, this is possible by arranging a temperature transducer within the tank for monitoring the milk temperature in the tank and controlling said cooling equipment such, that the cooling power is reduced to a minimum when the milk temperature is decreasing and approaching a value in an interval between +6 and +10xc2x0 C.
Preferably, this can be achieved by deactivating the cooling equipment when the milk temperature is approaching a value in an interval between +3 and +4xc2x0 C.
Advantageously, this is possible by reactivating the cooling equipment when the milk temperature is increasing and approaching a value in an interval between +6 and +10xc2x0 C.
Preferably, this is performed by arranging a means for measuring and monitoring the milk quantity in the tank and deactivating said cooling equipment when the milk quantity is insufficient for a regular agitator means to work properly.
Advantageously, the input means comprises a first agitation pipe having a first end and a second end, which agitation pipe at said first end is attached to and extended through a regular milk outlet in said first end wall and said second end being formed with said nozzle end.
Suitably, the position, at which the incoming milk is introduced to the milk contacting surface, is further determined by means of the nozzle end being located at a predetermined height over the lowest part of said bottom wall portion.
Advantageously, a spacer means is arranged to separate the nozzle end from said bottom wall portion.
Preferably, said input means comprises a second agitation pipe, which is correspondingly arranged in the second end wall opposite to said first agitation pipe in the first end wall of the tank.
Suitably, said input means comprises a pump means, which is embodied of the milk pump of the end unit in a milking system.
Advantageously said input means comprises an additional pump means.
Preferably, said additional pump means is comprised of a circulation pump of the centrifugal type.
Suitably, said circulation pump is of the submersible type and located inside the tank.
Advantageously, the circulation pump is arranged to draw milk from the pool at the lowest part of the bottom wall portion.
Preferably, the circulation pump is driven by means of a long drive shaft and a driving motor mounted on top of the tank.
Suitably, the additional pump means comprises a pump of the injector type driven by means of the pressure from the milk pump.
Advantageously, the additional pump means comprises an external circulation pump, the inlet of which being associated with the outlet of the tank.
Preferably, said external circulation pump is provided with a return line, which is passing over the top side of the tank and the uppermost part of which being provided with a vacuum-connected chamber, for returning milk from said outlet to the tank.
Suitably, said return line, downstream of said chamber, is connected to the agitation pipe via a first check valve.
Advantageously, said external circulation pump is omitted and said first check valve being arranged for interacting operation with a second check valve, by means of a three way valve at said vacuum-connection to said chamber.
Preferably, said chamber is located at a level, which is lower than the top of the tank.
Suitably, said return line, downstream of said chamber, is connected to the agitation pipe via a third check valve and is associated with said outlet of the tank by means of a fourth check valve, said check valves being arranged to interact such, that a flow would be allowed in the direction from the fourth to the third check valve only.
Advantageously, a milk transport line, by means of fourth and fifth valve means, is connectable to either said vacuum chamber or an accumulation chamber, which is located at a higher level than said vacuum chamber.
Preferably, first, second and third milk transport lines are connectable to said accumulation chamber, by means of correspondingly arranged fifth valve means.
Further features of advantageous embodiments and developments appear from the following description.